Astronomers have gotten quite skilled at detecting stars, but the much smaller and less luminous planets still present a problem: our current instruments simply aren’t sensitive enough. Nevertheless, we have learned a few things from the sample we do have. Figures estimate something in the range of 1.6 planets for every star in the Milky Way. With an estimated 100 billion stars, that’s quite a lot of planets, although we have only found less than 800.

On this day, October 19, in 2009, in one of the biggest recent astronomical discoveries, scientists announce a treasure trove of new planets — 32 in all — found via the HARPS spectrograph in Chile.

The Spectrograph, called the High Accuracy Radial Velocity Planet Searcher, seeks out planets by looking for ever-so-slight dimming of the starlight, indicating the passage of a planet between the star and earth. So far the vast majority of the planets found in this way have been giants, many times the size of Jupiter, but the sample is skewed because smaller planets are harder to find.